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arXiv2019

Erwin L. Hahn: A Biographical Memoir

Erwin Louis Hahn was one of the most innovative and influential physical scientists in recent history, impacting generations of scientists through his work in nuclear magnetic resonance (NMR), optics, and the intersection of these two fields. Starting with his discovery of the spin echo, a phenomenon of monumental significance and practical importance, Hahn launched a major revolution in how we think about spin physics, with numerous implications to follow in many other areas of science. Students of NMR and coherent optics quickly discover that many of the key concepts and techniques in these fields derive directly from his work.

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arXiv2019

Historical and Philosophical Aspects of the Einstein World

This article presents a brief review of some historical and philosophical aspects of Einstein's 1917 paper 'Cosmological Considerations in the General Theory of Relativity', a landmark work that denoted the starting point of modern theoretical cosmology. Our presentation includes a discussion of Einstein's early views of issues such as the relativity of inertia, the curvature of space and the cosmological constant. Particular attention is paid to lesser-known aspects of Einstein's paper such as his failure to test his model against observation, his failure to consider the stability of the model and a slight mathematical confusion concerning the introduction of the cosmological constant term. Taken in conjunction with his later cosmological works, we find that Einstein's approach to cosmology was characterized by a pragmatic search for the simplest model of the universe that was consistent with the principles of relativity and with contemporaneous astronomical observation.

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arXiv2019

Refuting Strong AI: Why Consciousness Cannot Be Algorithmic

While physicalism requires only that a conscious state depends entirely on an underlying physical state, it is often assumed that consciousness is algorithmic and that conscious states can be copied, such as by copying or digitizing the human brain. In an effort to further elucidate the physical nature of consciousness, I challenge these assumptions and attempt to prove the Single Stream of Consciousness Theorem (SSCT): that a conscious entity cannot experience more than one stream of consciousness from a given conscious state. Assuming only that consciousness is a purely physical phenomenon, it is shown that both Special Relativity and Multiverse theory independently imply SSCT and that the Many Worlds Interpretation of quantum mechanics is inadequate to counter it. Then, SSCT is shown to be incompatible with Strong Artificial Intelligence, implying that consciousness cannot be created or simulated by a computer. Finally, SSCT is shown to imply that a conscious state cannot be physically reset to an earlier conscious state nor can it be duplicated by any physical means. The profound but counterintuitive implications of these conclusions are briefly discussed.

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arXiv2019

Theoretical Equivalence and Duality

Theoretical equivalence and duality are two closely related notions: but their interconnection has so far not been well understood. In this paper I explicate the contribution of a recent schema for duality to discussions of theoretical equivalence. I argue that duality suggests a construal of theoretical equivalence in the physical sciences. The construal is in terms of the isomorphism of models, as defined by the Schema. This construal entails interpretative constraints that should be useful for theoretical equivalence more generally. I illustrate the construal in various formulations of Maxwell's electromagnetic theory.

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arXiv2019

Falsifiability of Isolated Spacetime Regions

In this work it is pointed out that some physical theories, even being themselves falsifiable, predict the existence of regions of spacetime which are not falsifiable with relation to each other due to their impossibility of mutually exchanging information as, for instance, before and after the event horizon of black holes. If we require scientific theories to be falsifiable, an isolated region should be discarded from scientific models developed by observers in other regions. Here it is proposed that their existence can satisfy a weaker falsifiability condition, here called conditional asymptotic provability, which extend scientific reasoning through Bayesian inference. Limitations and some epistemic consequences of this proposal are discussed.

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arXiv2019

Quantum Mechanics of Individual Systems

A formulation of quantum mechanics, which begins by postulating assertions for individual physical systems, is given. The statistical predictions of quantum mechanics for infinite ensembles are then derived from its assertions for individual systems. A discussion of the meaning of the "state" of an individual quantum mechanical system is given, and an application is made to the clarification of some of the paradoxical features of the theory.

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arXiv2019

Physics and the Totalitarian Principle

What is sometimes called the "totalitarian principle," a metaphysical doctrine often associated with the famous physicist Murray Gell-Mann, states that everything allowed by the laws of nature must actually exist. The principle is closely related to the much older "principle of plenitude." Although versions of the totalitarian principle are well known to physicists and often appear in the physics literature, it has attracted little reflection. Apart from a critical examination of the origin and history of the totalitarian principle, the paper discusses this and the roughly similar plenitude principle from a conceptual perspective. In addition it offers historical analyses of a few case studies from modern physics in which reasoning based on the totalitarian principle can be identified. The cases include the prediction of the magnetic monopole, the hypothesis of radioactive protons, and the discovery of the muon neutrino. Moreover, attention is called to the new study of metamaterials.

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arXiv2019

Theorie der Electrophorese -- Het Relaxatie-Effect

In this thesis, a theoretical treatment of the relation between electrophoretic velocity and the potential of the double layer of colloidal particles is presented. Translators' note: The theory of electrophoresis is one of the foundational topics that underpinned the development of colloid and surface science and ranks with the famous Derjaguin-Landau-Verwey-Overbeek (DLVO) theory of colloidal stability. J. Th. G. Overbeek ("Theo" to all who knew him) was the first to develop a complete theoretical analysis of the electrophoretic motion of a charged spherical particle under the influence of an external electric field. This provided the theoretical framework for a widely used experimental method to characterize the state of charge and particle size of small colloidal particles. The solution of this problem required mastery of fluid mechanics, colloidal electrostatics, statistical thermodynamics and transport theory in addition to solid applied mathematics. Theo carried out this study as his doctoral thesis under H.R. Kruyt at Utrecht University. The thesis, in Dutch, was later published as a monograph. Given the important pedagogic value and historical status of this work, we felt that it deserved to enjoy a wide readership.

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arXiv2019

Neutrino Physics in Historical Context

This contribution aims to give an overview of the historical context of neutrino physics. I will present the strong social trends that shaped physics and the way physicists worked, along the 20th century. First, we will see the background of the birth of nuclear physics in the interwar period. Then, we will examine the deep implications the Second World War had, to conclude with the specificities of postwar years for nuclear and particle physics.

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arXiv2019

Time travelling in emergent spacetime

Most approaches to quantum gravity suggest that relativistic spacetime is not fundamental, but instead emerges from some non-spatiotemporal structure. This paper investigates the implications of this suggestion for the possibility of time travel in the sense of the existence of closed timelike curves in some relativistic spacetimes. In short, will quantum gravity reverse or strengthen general relativity's verdict that time travel is possible?

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arXiv2019

Some remarks on history and pre-history of Feynman path integral

One usually refers the concept of Feynman path integral to the work of Norbert Wiener on Brownian motion in the early 1920s. This view is not false and we show in this article that Wiener used the first path integral of the history of physics to describe the Brownian motion. That said, Wiener, as he pointed out, was inspired by the work of some French mathematicians, particularly Gateaux and Levy. Moreover, although Richard Feynman has independently found this notion, we show that in the course of the 1930s, while searching a kind of geometrization of quantum mechanics, another French mathematician, Adolphe Buhl, noticed by the philosopher Gaston Bachelard, had himself been close to forge such a notion. This reminder does not detract from the remarkable discovery of Feynman, which must undeniably be attributed to him. We also show, however, that the difficulties of this notion had to wait many years before being resolved, and it was only recently that the path integral could be rigorously established from a mathematical point of view.

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arXiv2019

Sudarshan Memorial Lecture

In this invited talk, I discuss four important contributions of E.C.G. Sudarshan, among many. They are the V-A theory of weak interaction, Sudarshan - Glauber representation, tachyons and the quantum zeno effect.

physics.hist-ph↗

arXiv2019

Music of the Spheres: Teaching Quantum Field Theory at the Introductory Level

Quantum field theory has formed the conceptual framework of most of physics for more than sixty years. It incorporates a complete revision of our conception of the nature of matter and existence itself. Yet it is rarely taught, or even mentioned, in introductory physics---from high school, college, and university survey courses through upper-division "modern physics" courses. This omission is not necessary: This paper describes an approach through which the fundamental concepts and consequent insights of quantum field theory can be grasped, building upon familiar notions from classical and quantum mechanics.

physics.hist-ph↗

arXiv2019

"Sufficiently Advanced Technology" for Gravitational Wave Detection

The science fiction writer Arthur C. Clarke wrote, "Any sufficiently advanced technology is indistinguishable from magic." While not magical by any means, the technology used to detect gravitational waves starting in 2015 is surely sufficiently advanced to be remarkable by any ordinary standard. That technology was developed over a period of almost six decades; the people who were directly involved numbered in the thousands. In this article, I give an idiosyncratic account of the history, with a focus on the question of how people learned what measurement technology would be "sufficiently advanced" to succeed in detecting gravitational waves.

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arXiv2019

En busca de los efectos gravitacionales de Birkhoff: la ultracentrıfuga transelastica

This work reviews the origin, development, completion, and outcome of a trans-elastic ultracentrifuge project of Mexico's Nuclear Center through 1971 to 1986. The project had its origin in the search for an effect that supposedly would validate Birkhoff's gravity theory over Einstein's General Relativity. For this purpose an extraordinary ultracentrifuge was built which deserved the 1973 National Award for Instruments (Mexico). The ultracentrifuge was also used to investigate the feasibility of uranium enrichment by solid state centrifugation. Highly enriched uranium was obtained, but in small quantities.

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arXiv2019

An "anti-system" ontology of quantum physics, as derived from two Einstein's conceptions of physical theories. Quantum physics as a theory of general relativity of experimental context

In glaring contrast to its indisputable century-old experimental success, the ultimate objects and meaning of quantum physics remain a matter of vigorous debate among physicists and philosophers of science. This article attempts to shed new light on the debate. It relies upon two comments by Albert Einstein on his general approach to physical theories. I draw their consequences for the definition of a physical theory's ontology, and next for the ontology of quantum physics - i.e. what it may ultimately be about. The quantum ontology thus derived appears to be strictly limited to evolving experimental contexts and instantaneous measurement outcomes, which are to be understood, respectively, as mere potential measurement outcomes and actual ones. The notions of material body in particular and physical system in general are absent from this ontology, hence the vanishing of Schroedinger's cat and EPR paradoxes, as well as of the quantum measurement problem. Apart from its ability to clear up well-known conundrums, this ontology reveals what quantum physics may fundamentally be - i.e. its possible ultimate meaning - namely a theory of general relativity of experimental context. On this basis, I conclude with a new conception of objectivity in the sciences of nature.

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arXiv2019

Paisaje celeste y arqueoastronomía: las iglesias históricas como indicadores de la planimetría de una ciudad ideal

According to popular tradition, the Canarian city of San Cristobal de La Laguna, a World Heritage Site by UNESCO since 1999, emerged in the early sixteenth century with a novel organization, in line with a new peaceful social order inspired by the religious doctrine of the millennium and its expression through urban design [...] In this paper we briefly discuss some details of these ideas, which propose a planned geometric origin for the city, and the original sources on which they are based. We then look for other indications that in a simpler way might explain some of the notable characteristics of the order and design of La Laguna, where over time a model of traditional Canarian architecture was installed that, during the 17th century, was populated with civil and religious constructions (churches, chapels and convents) with notable creations in carpentry of Mudejar origin, for example coming from the lower Andalusia. To conclude, we show our precise analysis of the orientation of almost all the historical churches and chapels of the city, taken together as an indicator of its planimetry. This study employs the usual tools of archaeoastronomy as a complement to the historical and cultural research of religious constructions. We will see then that a new -- and simpler -- interpretation of the spatial distribution of the city is possible.

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arXiv2019

Oral History Interview with Marcello Cresti

Marcello Cresti graduated in Physics in 1950 at the University of Pisa by attending the Scuola Normale Superiore; he became professor of Experimental Physics in Padua in 1965, and then Rector of the University of Padua in 1984. His research was focused on the physics of cosmic rays and elementary particles; he started collaborations with research laboratories in Berkeley, Geneva, and with Max-Planck Institutes, which influenced the evolution of research on fundamental physics.

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